Apparatus for the extrusion of cellular synthetic resins

ABSTRACT

Apparatus for the extrusion of cellular (foamed) synthetic resins and elastomers in which a masticated and plastified synthetic resin or elastomer mixture, blended with a foaming agent, is extruded through a nozzle, e.g., in the form of slab. The extruded slab is permitted to expand against a superatmospheric counterpressure during cooling in one or more chambers provided immediately ahead of the extrusion nozzle, the chambers being separated from one another by pressure-retaining gates or locks. Between each chamber, a driven or autorotating pair of calibrating rolls may form part of the pressure-retaining gate.

United States Patent Reifenhauser et al.

[ 1 Mar. 7, 1972 APPARATUS FOR THE EXTRUSION OF CELLULAR SYNTHETICRESINS Fritz Reifenhauser; Hans Reilenhauser, both of Troisdorf; KlausBurggrai, Sieglar, all of Germany Assignee: Reiienhauser KG, Troisdorf,Germany Filed: Aug. 4, 1969 Appl. No.: 847,085

inventors:

Foreign Application Priority Date Aug. 3, 1968 Germany ..P 17 79 374.7

US. Cl ..425/4, 264/54, 264/55,

264/89, 425/363, 425/817 Int. Cl ..B29d 27/00 FieldofSearch..18/1F,4S,4B, 19TM, 12 P,

18/12 TF, 5 F, 5 P, 9; 264/53, 89, 348, 54, 55

I561 fts- 999i!!! UNITED STATES PATENTS 2,401,642 6/1946 Hiltner..264/348 X 3,119,147 1/1964 Kracht ..l8/l

Primary Examiner-J. Spencer Overholser Assistant Examiner-Norman E.Lehrer Attorney-Karl F. Ross [57] ABSTRACT Apparatus for the extrusionof cellular (foamed) synthetic resins and elastomers in which amasticated and plastified synthetic resin or elastomer mixture, blendedwith a foaming agent, is extruded through a nozzle, e.g., in the form ofslab.

The extruded slab is permitted to expand against a superatmosphericcounterpressure during cooling in one or more chambers providedimmediately ahead of the extrusion nozzle, the chambers being separatedfrom one another by pressure-retaining gates or locks. Between eachchamber, a driven or autorotating pair of calibrating rolls may formpart of the pressure-retaining gate.

3 Claims, 2 Drawing Figures APPARATUS FOR THE EXTRUSION OF CELLULARSYNTHETIC RESINS FIELD OF THE INVENTION Our present invention relates toan apparatus for the extrusion of cellular or foamed synthetic resinsand elastomers and, more particularly, to a system for the formation ofprecisely dimensioned slabs sheets or layers of such materials.

BACKGROUND OF THE INVENTION It is a common practice in the formation ofsynthetic-resin bodies and especially flexible or rigid cellular orfoamed synthetic resins (thermoplastics) and elastomers, to form anexpanding mixture of the thermoplastic base material in a plastificationand mastication assembly by incorporating in the thermoplastic, afoaming agent or providing in homogeneous dispersion therein, an agentcapable of generating gas upon extrusion of the mixture through anozzle.

The foaming agent may be a gas or a liquid which is intimately blendedwith the thermoplastic material and/or dis solved therein at thepressure developed during mastication and capable of expanding againstatmospheric pressure at the extrusion temperatures, i.e., a substance(generally a fluid) having a vapor pressure at the extrusion temperaturein excess of atmospheric pressure or a boiling point below the extrusiontemperature.

It has also been proposed to provide foaming or expanding agents whichoperate by chemical reaction to produce gas upon extrusion. It may benoted at this point that the present invention relates to all suchsystems for thermoplastic materials and forming cellular bodies withopen or closed pores.

In connection with the formation of slabs, plates or layers of suchmaterials, it has been the practice heretofore to permit the extrudedsheet to expand against ambient (atmospheric) pressure and thereafterimpart the desired dimensions and density to the slab by passing thelatter through one or more sets of calendering rolls in a separateoperation. Such arrangements are expensive and, since they operate upona fully expanded slab, frequently do not achieve the desired results interms of imparting precise dimensions to the slab.

OBJECT OF THE INVENTION It is, therefore, the principal object of thepresent invention to provide an improved method and an improvedapparatus for the formation of extruded cellular bodies of theaforementioned character which are free from the above-mentioneddisadvantages and have precisely controllable dimensions.

SUMMARY OF THE INVENTION This object and others, which will be apparenthereinafter, are achieved, in accordance with the present invention, bya system for the extrusion of slabs of expandable synthetic resin, i.e.,a masticated and plastified thermoplastic mixture containing anexpanding agent, wherein the slab is extruded through a noule directlyinto a pressure chamber in which a counterpressure above atmospheric ismaintained and at least an initial cooling of the slab is carried out tolimit expansion of the slab.

According to a more specific feature of this invention, two or morechambers are provided in succession between the nozzle and theatmosphere and expansion of the continuously extruded body traversingthese chambers is effected in two or more stages. By controlling thepressure, it is possible to precisely dimension the body and carefullyregulate the degree of expansion.

An important aspect of this invention resides in the cooling of thethermoplastic body prior to emergence from the last pressure chamber tothe point at which further expansion cannot occur.

Still another feature of this invention resides in the provision ofprecisely calibrated gaps at the inlet side of the first pressurechamber, between successive pressure chambers and at the outlet side ofthe final pressure chamber, thereby assuring the precise dimensioning ofthe body. In accordance with this feature, we provide pressure-retentivelocks or gates between the pressure chambers and at the inlet and outletsides of the first and last chambers which function as the calibratedslots or openings through which the continuously extruded body passes.

More specifically, these slots can be designed between sets ofcalibrating rolls which also form part of the pressure-retentive gates,although it is obvious that simple calibrating openings without suchrolls may be provided. When the rolls are used, they may be driven toprovide a calendering effect or may be autorotating, i.e., rotated bythe continuous extruded body as its drawn between the rolls. The fluidcirculated through the pressure chambers, to maintain the desiredpressure levels, may also serve as the cooling medium in contact withwhich the extruded body solidifies.

The system described above thus affords the ability of controllingfoamed thermoplastics within narrow limits to impart desired dimensionsto them with small tolerances and eliminates separate processing ofpreformed extruded bodies in calendering-roll arrangements or the like.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description, reference being made to the accompanyingdrawing in which:

FIG. 1 is a diagrammatic sectional view through an apparatus, accordingto the present invention; and

FIG. 2 is a plan view thereof.

SPECIFIC DESCRIPTION In the drawing, we have shown an arrangement whichcomprises a plastified or masticating worm membly l of conventionalconstruction which thoroughly blends under pressure and usually withtemperature elevation, a thermoplastic mass (e.g., polystyrene) to whichan expanding agent (e.g., a hydrocarbon, a fluorocarbon or carbondioxide) has been added to form a flowable, expandable thermoplasticblend which is extruded through an extrusion nozzle or die 2, herehaving a slotlike opening designed to form a slab 20.

According to the present invention directly ahead of the nozzle or die2, i.e., without an intervening gap open to the atmosphere, is provideda pressure chamber 6 maintained at a superatmospheric pressure justabove or slightly below the vapor pressure of the expanding agent at theextrusion temperature. A pressure gauge 21 serves to indicate thepressure and fluid circulated through the chamber 6 is provided and isrepresented by arrows 22 and 23. Consequently, substantially nosignificant expansion of the extruded sheet 20a, emerging from thenozzle, occurs.

The chamber 6 is formed in a housing 3 which is mounted upon the nouleor die 2 and constitutes a calibrating device for controlling thethicknesses of the slab. The first slab 20 is drawn from the calibratingdevice 3 between a pair of conveyor bands 4 and 5 so that the rolls ofthe calibrating devices need not be driven although motors may beprovided as represented at 24 for operating these rolls.

Immediately ahead of the first stage pressure chamber 6, there isprovided within the housing of the calibrating device 3, a secondpressure chamber 7 which is maintained at a slightly lower pressure (II)as indicated by the gauge 25 and is supplied with the cooling andpressurizing gas (e.g., air) as represented at 26 and 27.

Between the pressure chambers 6 and 7, there is provided a pressure lockor gate in the form of a pair of walls 11 which sealingly bear againstthe surfaces of a pair of initial calibrating rolls 9 and 10, the lattersqueezing the sheetsbetween them.

Within chamber 7, the slab portion 20b expands to a greater thickness(FIG. 1) precisely determined by the pressure within this chamber and ispassed thereafter through a gate formed by the walls 12 and the rolls l3and 14, into the next chamber 8.

At the exit side of this chamber, which has a pressure gauge 29 and issupplied with cooling fluid as represented by the arrows 30 and 31 tomaintain a slightly lower pressure above atmospheric, there is providedthe final pair of rolls l5 and 16 cooperating with walls 32 to fonn thefinal pressure gate. The slab, which expands further at portion 26 inchamber 8, passes between rolls l5 and 16 but is now in a fully hardenedor cooled state so that no further expansion may occur except for theslight expansion which results when the external pressure on the slab isrelieved. A precise dimensioning of the slabs has been found to bepossible with this device.

SPECIFIC EXAMPLE Polystyrene, which contained no blowing agents, wassupplied with 1.4 percent of sodium bicarbonate and 1.6 percent ofsodium citrate while it was fed into the hopper of the extruder. Themixture was then heated to 176 C. while it flowed through the extruder.In the path of molten polystyrene 7 percent of pentane was added under11 kg./cm. pressure continuously to be well mixed with the moltenpolystyrene, and the mixture was cooled at 127 C. and then heated at 121C. The heated mixture was then extruded through the die into a firstchamber at a pressure of kg./cm. (gauge), a second chamber at 5 kg./cm.(gauge) and a third chamber at l kg./cm. (gauge) prior to emergence intothe atmosphere at a temperature of about 80 C.

We claim:

1. An apparatus for the extrusion of a foamed thermoplastic syntheticresin comprising an extrusion press having an extrusion die forextruding a continuous body of foarnable thermoplastic synthetic resin;housing means sealingly connected to said die and defining a pluralityof chambers immediately ahead of said die and successively traversed bysaid body, said chambers including a first pressure chamber extendingfrom said die and second and third pressure chambers successivelydownstream of said first chamber; pressure-control means connected toeach of said chambers for adjusting the pressure therein to .control theexpansion of said body; and a pressureretentive gate formed in saidhousing means between a pair of successive chambers, said gatecomprising a partition wall formed on said housing means on oppositesides of said body and extending toward said body but terminating shortof respective surfaces of said body to define gaps therewith, andrespective rolls journaled in said housing means and sealinglyobstructing said gaps while rollingly engaging said body for calibratingsame.

2. The apparatus defined in claim 1, further comprising a further pairof calibrating rolls defining an outlet gate in said housing means andengaging said body for calibration thereof upon feeding said body out ofsaid housing means.

3. The apparatus defined in claim 1, further comprising a pair ofcalibrating rolls immediately adjacent said die and sealingly engagingsaid body upon entry thereof into said housing means.

1. An apparatus for the extrusion of a foamed thermoplastic syntheticresin comprising an extrusion press having an extrusion die forextruding a continuous body of foamable thermoplastic synthetic resin;housing means sealingly connected to said die and defining a pluralityof chambers immediately ahead of said die and successively traversed bysaid body, said chambers including a first pressure chamber extendingfrom said die and second and third pressure chambers successivelydownstream of said first chamber; pressure-control means connected toeach of said chambers for adjusting the pressure therein to control theexpansion of said body; and a pressure-retentive gate formed in saidhousing means between a pair of successive chambers, said gatecomprising a partition wall formed on said housing means on oppositesides of said body and extending toward said body but terminating shortof respective surfaces of said body to define gaps therewith, andrespective rolls journaled in said housing means and sealinglyobstructing said gaps while rollingly engaging said body for calibratingsame.
 2. The apparatus defined in claim 1, further comprising a furtherpair of calibrating rolls defining an outlet gate in said housing meansand engaging said body for calibration thereof upon feeding said bodyout of said housing means.
 3. The apparatus defined in claim 1, furthercomprising a pair of calibrating rolls immediately adjacent said die andsealingly engaging said body upon entRy thereof into said housing means.